Nuclear Waste Assessment System for

Technical Evaluation (NUWASTE):

Status and Initial Results

A Report to the U.S. Congress

and the Secretary of Energy

U.S. Nuclear Waste Technical Review Board

June 2011

Topical Report #2
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U.S. Nuclear Waste Technical Review Board

Report Availability

This report and other reports by the NWTRB are available on the

Board’s Web site at: www.nwtrb.gov
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Nuclear Waste Assessment System for Technical Evaluation (NUWASTE) Status and Initial Results
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U.S. Nuclear Waste Technical Review Board

Authors

This report presents results from work completed as part of the

U.S. Nuclear Waste Technical Review Board’s analysis of the

impact of alternative fuel-cycle initiatives on the generation of

spent nuclear fuel and high-level radioactive waste. The effort is

led by Dr. Mark D. Abkowitz, Board member. This report was

prepared by Mr. Nigel Mote, Mr. Gene W. Rowe, and Dr. Bruce E.

Kirstein, members of the Board’s staff.
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Nuclear Waste Assessment System for Technical Evaluation (NUWASTE) Status and Initial Results

U.S. Nuclear Waste Technical Review Board

B. John Garrick, Ph.D., P.E.; Chairman

Consultant

Newport Beach, California

Mark D. Abkowitz, Ph.D.

Vanderbilt University

Nashville, Tennessee

Wm. Howard Arnold, Ph.D., P.E.

Consultant

Macatawa, Michigan

Thure E. Cerling, Ph.D.

University of Utah

Salt Lake City, Utah

David J. Duquette, Ph.D.

Rensselaer Polytechnic Institute

Troy, New York

George M. Hornberger, Ph.D.

Vanderbilt University

Nashville, Tennessee

Andrew C. Kadak, Ph.D.

Exponent Corporation

Natick, Massachusetts

Ronald M. Latanision, Ph.D.

Exponent Corporation

Natick, Massachusetts

Ali Mosleh, Ph.D.

University of Maryland

College Park, Maryland

William M. Murphy, Ph.D.

California State University

Chico, California

Henry Petroski, Ph.D., P.E.

Duke University

Durham, North Carolina
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U.S. Nuclear Waste Technical Review Board

Nuclear Waste Technical Review Board Staff

Executive Staff

Nigel Mote, Executive Director

Joyce M. Dory, Director of Administration

Technical Staff

Carlos A. W. Di Bella, Senior Professional Staff

David M. Diodato, Senior Professional Staff

Bruce E. Kirstein, Senior Professional Staff

Daniel S. Metlay, Senior Professional Staff

Douglas B. Rigby, Senior Professional Staff

Gene E. Rowe, Senior Professional Staff

External Affairs Staff

Karyn D. Severson, Director

Information Technology Staff

William D. Harrison, Systems Administrator

Administrative & Support Staff

Davonya S. Barnes, Information Systems Specialist

Linda J. Coultry, Program Support Specialist

Linda L. Hiatt, Management Analyst
Summary

The U.S. Nuclear Waste Technical Review Board (Board) has

developed a computer-based systems analysis tool called the

Nuclear Waste Assessment System for Technical Evaluation

(NUWASTE). The Board intends to use NUWASTE to support its

ongoing technical evaluation of U.S. Department of Energy (DOE)

activities related to the management of spent nuclear fuel (SNF)

and high-level radioactive waste1 (HLW). Initial analyses

performed using NUWASTE have demonstrated its value in

gaining a better understanding of the effects of potential fuel-cycle

initiatives on the generation of SNF, HLW, and other waste

streams. A particularly important feature of NUWASTE is its

ability to compare results for a range of scenarios and quantify the

relative impacts on the program for managing SNF and HLW in

the United States.

NUWASTE currently is designed to assess alternative fuel-cycle

scenarios for the existing fleet of U.S. light-water reactor (LWR)

nuclear power plants and the additional LWRs for which license

applications have been submitted to the U.S. Nuclear Regulatory

Commission (NRC). The initial focus of the NUWASTE analyses

has been on the management of the SNF generated by those LWR

plants, including dry storage, direct disposal in a repository, and

the potential introduction of reprocessing with recycling of

uranium and plutonium.

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Nuclear Waste Assessment System for

Technical Evaluation (NUWASTE):

Status and Initial Results

Nuclear Waste Assessment System for Technical Evaluation (NUWASTE) Status and Initial Results

1. A glossary of technical terms and abbreviations is provided at the end of this report.
This report presents the results of analyses performed on four

scenarios for managing SNF and HLW. The results reinforce the

need for a deep geologic repository for disposal of both SNF and

vitrified HLW in the United States and demonstrate that the

timing of the availability of such a repository will fundamentally

affect the need for additional SNF storage capacity. The results

also show that, for the existing LWR fleet and the additional LWRs

being considered by the NRC, the reprocessing scenarios

considered here would have limited benefit in reducing the

demand for natural uranium and limited benefit in reducing the

volume of SNF and HLW, while significantly increasing the

amount of low-level radioactive waste requiring disposal.

The Board is considering ways to extend this analysis and increase

the scope and functionality of NUWASTE. This effort includes

evaluating additional LWR scenarios and adding the capability to

show the relative effects of different scenarios on program costs

and operational timelines. Longer-term plans include expanding

the capability of NUWASTE to consider implications for SNF and

HLW management of introducing advanced thermal and fast

reactors, alternative reprocessing technologies and

away-from-reactor storage facilities, disposal of all DOE-owned

SNF and HLW, and transportation requirements at each stage of

the fuel cycle. As these developments are implemented, the Board

will continue to report the results of its analyses to Congress, the

Secretary of Energy, and the interested public.

U.S. Nuclear Waste Technical Review Board

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Introduction

The U.S. Nuclear Waste Technical Review Board2 (Board) was

created as an independent agency in the Executive Branch in the

1987 amendments to the Nuclear Waste Policy Act (NWPA). The

Board’s statutory responsibility is to conduct an independent and

ongoing evaluation of the technical activities undertaken by the

U.S. Department of Energy (DOE) in managing commercial,

research, and defense-related spent nuclear fuel (SNF) and

high-level radioactive waste (HLW) and to report its findings and

recommendations to Congress and the Secretary of Energy.

This report describes work being performed by the Board to

evaluate the effects of the various fuel-cycle options being

considered by DOE on the management of SNF and HLW. Of

particular interest to the Board are the types and quantities of the

radioactive waste streams that would be generated.

To support its technical evaluation of DOE’s work in this area, the

Board has developed the Nuclear Waste Assessment System for

Technical Evaluation (NUWASTE), a computer-based systems

analysis tool having the capability to analyze different scenarios

and to compare the results. The initial focus of the work

undertaken using NUWASTE has been on management of SNF

from the existing and planned light-water reactors (LWR),

including the potential introduction of reprocessing, and the

recycling of uranium and plutonium in the same population of

reactors. Coupled with this focus is consideration of the extent to

which the potential benefits of reprocessing and recycling could

currently be realized in practice in the United States. This is

fundamental in assessing SNF inventories, reprocessing and

recycling options, the radioactive waste streams that would be

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Nuclear Waste Assessment System for Technical Evaluation (NUWASTE) Status and Initial Results

2. Board members are nominated by the National Academy of Sciences and appointed by the

President to four-year terms. Members are supported by a full-time technical and

administrative staff headquartered in Arlington, Virginia.
generated, and the impact on demand for natural uranium.

Subsequently, the analysis will be expanded to include other

reactor technologies and the associated options for managing SNF

and HLW.

The Board is aware that other institutions, including universities,

National Laboratories, and private firms, are interested in

developing, and, in some cases, already have developed, related

analytical methods. However, the Board’s approach is designed

to provide an independent capability for evaluating the options

being considered by DOE. This approach focuses on the impact

each option would have on the types and quantities of radioactive

waste generated by the U.S. nuclear power program as a whole, in

line with the Board’s technical review mission.

Development of Systems Analysis Capability

Early in 2009, the Board recognized the need for the capability to

analyze the effects of new options for managing SNF and HLW

being considered by DOE on issues such as the following:

the need for dry storage of SNF at nuclear power plants

the volumes of SNF and HLW that would require disposal in

a repository

the reduction in uranium demand that would result from

recycling uranium and plutonium separated by reprocessing

the introduction of new waste streams from different

fuel-cycle technologies

The Board also knew that other factors must be taken into account,

such as the timescale for completing the disposition of the SNF

discharged from the existing and currently planned LWRs, and

the economic implications. This led to the development of

NUWASTE.

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U.S. Nuclear Waste Technical Review Board
NUWASTE presents material-balance results for the entire U.S.

nuclear power program. In this respect, it is different from most

other available analytical tools, which are focused mainly on

particular reactor types, management of a limited quantity of the

SNF that will be discharged, or the effect of a particular process

technology.

NUWASTE currently includes data on the complete U.S. fleet of

operating and presently planned LWRs and all of the fuel-cycle

operations needed to produce new fuel and manage SNF.3 It also

projects the quantities of waste of each type generated from

reprocessing. A wide range of SNF management strategies,

nuclear generation capacities, and fuel-fabrication alternatives can

be represented. For example, the start date, capacity, and

operating periods of the SNF management and waste disposal

facilities can be specified, along with fuel burn-ups and the order

of selection of SNF for disposal and reprocessing. NUWASTE also

has the capability to apply importance-weighting to different

waste management impacts when comparing the implications of

alternative SNF and HLW management scenarios.

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Nuclear Waste Assessment System for Technical Evaluation (NUWASTE) Status and Initial Results

3. Where fuel-cycle services are currently provided by companies operating in the nuclear fuel

markets on a commercial basis, no facility capacities or limits on availability are included in

NUWASTE. Where new facilities would need to be constructed to allow the introduction of

services that are not currently available, the facility capacities, and the timelines on which

they could realistically be expected to be brought into service, are included in NUWASTE.
Figure 1 presents a schematic of the LWR fuel-cycle operations

that NUWASTE currently is designed to address, including the

recycling of plutonium and uranium in LWRs4 and the wastes that

are generated. Each icon represents a facility, and each arrow

represents a potential transportation operation.

From examination of Figure 1, two important points become

apparent. First, the nuclear fuel cycle and waste management

facilities form a complex, interdependent system in which

fuel-cycle decisions can have a profound effect on, and be affected

by, waste management options. Second, a large number of LWR

scenarios can be defined by a unique combination of facility

capacities and operating timescales, the corresponding

transportation logistics and operations, and the assumptions that

underlie them.

Preliminary Analyses

For demonstrating NUWASTE functionality and illustrating the

waste-related effects associated with different SNF and HLW

management options, the results of four potential scenarios are

used as the basis for the discussions in the following sections.

Each scenario assumes the following:

The U.S. nuclear power plant fleet includes the existing

nuclear power plants plus the 25 plants for which license

applications have been submitted to the U. S. Nuclear

Regulatory Commission (NRC).

Each reactor has an operating life of 60 years, including

lifetime extensions.

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U.S. Nuclear Waste Technical Review Board

4. At present, NUWASTE does not include the waste generated during processing of uranium

ore to produce uranium hexafluoride, because this varies according to both the source of the

uranium ore and the extraction technology used and is thus not dependent only on the

fuel-cycle option selected. However, consideration is being given to adding this waste

stream to NUWASTE in the near future.
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Nuclear Waste Assessment System for Technical Evaluation (NUWASTE) Status and Initial Results

Figure 1. Process Operations and Material Flows Currently Included in NUWASTE
Fuel burn-up for fuel assemblies discharged before 2010 was

40 GWd/MT.

Fuel burn-up for fuel assemblies discharged in 2010 and

beyond will be 60 GWd/MT.

Scenario Definitions

The four scenarios analyzed here are defined as follows:

Scenario 1: Long-Term Storage Only

No repository

No reprocessing facility

Scenario 2: Direct Disposal of SNF

Repository operation starting in 2040 with a capacity of

3,000 MT/year

No reprocessing facility

Scenario 3: Recycling of Uranium and Plutonium

Reprocessing operations starting in 2030 with a capacity of

1,500 MT/year

Repository operations starting in 2040 with a capacity of

3,000 MT/year

Recycling of reprocessed uranium and plutonium once,

following separation during reprocessing5

All separated uranium and plutonium recycled within one

year

Scenario 4: Recycling of Plutonium Only

Same as Scenario 3 except that the separated uranium is not

recycled

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U.S. Nuclear Waste Technical Review Board

5. The value of the uranium and plutonium for production of new fuel decreases each time

they are recycled. For this analysis, it is assumed that neither will be recycled more than

once.
It is important to recognize that these scenarios are just four of

many that can be represented and evaluated using NUWASTE.

They were selected because they represent concepts that have

been widely discussed as options for managing the nuclear fuel

cycle and radioactive wastes from the current fleet of LWRs in the

United States. In addition, where reprocessing is included, the

reprocessing capacity was selected to allow for all of the separated

plutonium to be recycled in the LWRs before the end of their

operating lifetimes, without leaving any in storage that might

present a proliferation risk. The Board is planning to evaluate

other scenarios to gain a better understanding of the sensitivity of

the analysis results to different program characteristics, such as

facility capacities and operating schedules.

Methodology

The base module of NUWASTE includes a data library that

records the relevant specifications6 of all commercial nuclear

power plants currently operating in the United States, those that

have been permanently shut down, and those for which license

applications have been submitted to the NRC.7 The data library

also includes operator-provided information on the quantities of

all SNF discharged by those reactors and held in either wet or dry

storage through the end of 2009.8 The quantities of fuel that will be

discharged from the start of 2010 through the end of their

operating lifetimes are projected by NUWASTE on the basis of the

plant design and operating assumptions that are used to define a

particular scenario.

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Nuclear Waste Assessment System for Technical Evaluation (NUWASTE) Status and Initial Results

6. Source: NRC Information Digest, NUREG-1350, Appendix A.

7. Source: EIA Web site, Status of Potential New Commercial Nuclear Reactors in the United

States, www.eia.doe.gov/cneaf/nuclear/page/nuc_reactors/reactorcom.html.

8. Source: DOE TSM, TSMPP_SNF_Discharge_09_052809.xls.
On the basis of the assumed fuel burn-ups and initial enrichments,

NUWASTE calculates the masses of individual isotopes in the

spent-fuel assemblies that have been, or will be, discharged by the

operating and currently planned fleet of nuclear power plants.

The individual isotopes tracked by NUWASTE make up over 99

percent of the total fuel-assembly mass, including the major

uranium and plutonium isotopes along with another 54 isotopes

of fission-product elements and minor actinides.

The calculations of isotope masses in the SNF are made using the

ORIGEN9 computer code. On the basis of these calculations,

NUWASTE can project the mass of each isotope that will be

disposed of directly or separated during reprocessing for any

given scenario. In the reprocessing scenarios evaluated for this

report, NUWASTE does not reflect any particular separation

technology.

The uranium and plutonium in a fuel assembly are considered to

be separated completely into product streams, with the fission

products and minor actinides separated into a high-level

radioactive stream and a fission product gases waste stream.

These streams are shown in Figure 1, together with other waste

streams that are generated during reprocessing operations.

However, NUWASTE also has the flexibility to evaluate the more

realistic case where complete separation cannot be achieved (e.g.,

the plutonium product stream contains some small percentage of

uranium). This flexibility allows NUWASTE to project the effects

of using the processes available today and some of the more

advanced separation technologies being considered for potential

application in the future. In some of these cases, incomplete

separation of the uranium and plutonium maybe intended,

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U.S. Nuclear Waste Technical Review Board

9. ORIGEN/SCALE 6.0 (Oak Ridge Isotope GENeration/ Standardized Computer Analyses for

Licensing Evaluation) is a computer code developed at Oak Ridge National Laboratory to

calculate the inventories of fission products and minor actinide elements in SNF discharged

after irradiation in a reactor.
possibly with some of the fission-product or minor actinide

materials also included in the combined product stream, to meet

nonproliferation objectives.

On the basis of the quantities of materials in each product stream,

NUWASTE then calculates the quantities of recycled fuel that can

be fabricated for loading into reactors each year. It also calculates

the volumes of HLW and other wastes that would be generated

each year, adding them to the inventories requiring disposal. In

each year, the maximum number of disposal waste packages

containing SNF and HLW to be emplaced in a repository is

projected.

Results

Using NUWASTE to assess the four scenarios considered in this

report produced several notable insights.

Requirement for Dry-Storage Casks

Figure 2 shows the number of dry-storage casks required in each

scenario. Absent a repository or a recycling program (Scenario 1),

a total of more than 12,000 dry-storage casks will be required by

the year 2100, each holding on average either 32

pressurized-water reactor (PWR) fuel assemblies or 68

boiling-water reactor (BWR) fuel assemblies.10 The availability of

a repository having a disposal capacity of 3,000 MT/year

(Scenario 2), possibly combined with a reprocessing facility with a

capacity of 1,500 MT/year (Scenarios 3 and 4), could significantly

reduce the total number of dry-storage casks required, the size of

the reduction depending on the facility receipt rates and start

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Nuclear Waste Assessment System for Technical Evaluation (NUWASTE) Status and Initial Results

10.Dry-storage casks with capacities of 32 PWR and 68 BWR are assumed for the purpose of

these calculations and are representative of storage systems that currently are used by many

utilities.
dates. However, as can be seen in Figure 2, even under the

optimistic conditions assumed in Scenarios 3 and 4, more than

6,000 dry-storage casks still would be required.

Demand for Repository Disposal Waste Packages

Figure 3 shows the number of repository disposal waste

packages11 required in each scenario and the timeline over which

they accumulate. Because there is no repository in Scenario 1, no

disposal packages are required. Comparison of the results for the

other scenarios allows the following observations to be made:

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U.S. Nuclear Waste Technical Review Board

Figure 2. Number of Dry-Storage Casks Required

11.A repository disposal waste package may contain either SNF or HLW and is designed for

emplacement in a repository for final disposal.
Addition of a 1,500 MT/year reprocessing facility in Scenarios

3 and 4 to the repository included in Scenario 2 reduces the

number of disposal waste packages required by

approximately 30 percent.

Despite this reduction, reprocessing does not remove the need

for a repository.

If reprocessing operations start before repository operations

(as assumed in Scenarios 3 and 4), HLW canisters from

reprocessing will start to accumulate before the repository can

receive them for disposal, and storage capacity will need to be

provided.

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Nuclear Waste Assessment System for Technical Evaluation (NUWASTE) Status and Initial Results

Figure 3. Number of Disposal Waste Packages Required
Demand for Natural Uranium

Another aspect of introducing reprocessing and recycling that can

be analyzed using NUWASTE is the extent to which the demand

for natural uranium would be reduced. Figure 4 shows that when

both reprocessed uranium and plutonium are recycled once, as in

Scenario 3, the effect is roughly a 14 percent reduction in the

amount of natural uranium required when compared with

Scenarios 1 and 2.12 However, fuel assemblies with burn-ups of

greater than approximately 55 GWd/MT have 236U concentrations13

that would require the reprocessed uranium to be enriched above

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U.S. Nuclear Waste Technical Review Board

Figure 4. Natural Uranium Requirement

12.This reduction in uranium requirement results from the introduction of a reprocessing

capacity of 1,500 MT/year in 2030. Increasing the reprocessing capacity potentially would

result in an additional reduction in uranium requirement. However, there are practical

limits on the extent to which uranium and plutonium can be recycled, and this will be the

subject of further analysis using NUWASTE.

13. 236U is an isotope of uranium produced during reactor operation. As it is a neutron

absorber, uranium containing 236U needs to be enriched to a higher 235U content than fresh

uranium if it is to be recycled into new fuel.
5.0 percent 235U, which is the present license limit, and therefore

would make the reprocessed uranium unsuitable for recycling in

LWRs. This would reduce the uranium savings to approximately

7 percent (Scenario 4).

Waste Streams

The choice of fuel-cycle strategy also affects the volumes and types

of wastes that would be generated in addition to HLW. Figure 5

shows the large quantity of low-level waste (LLW) and

Greater-Than-Class-C (GTCC) waste that would be generated by

reprocessing and repository operations.14 Scenario 1 does not

include a repository or a reprocessing facility, so no LLW or GTCC

waste is generated by these activities. In the other scenarios,

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Nuclear Waste Assessment System for Technical Evaluation (NUWASTE) Status and Initial Results

Figure 5. Quantity of LLW and GTCC Waste Generated

14.Source: Report FCRD-USED-2010-000033 Rev.0 “Low Level Waste Disposal – Quantities and

Inventory,” Savannah River Site report for DOE, June 2010.
a significant quantity of LLW is generated during facility

operations, the quantity generated during reprocessing (Scenarios

3 and 4) being far greater than that generated during direct

disposal of SNF (Scenario 2).

If the SNF received at a repository site or a reprocessing facility

needs to be unloaded from the canisters in which it is contained

for dry storage, additional quantities of LLW may be generated

from the disposal of these dry-storage canisters. However, not all

dry-storage systems use canisters, and some canisters may be able

to be used as inner containers in the disposal waste packages.

Consequently, there currently is no basis for projecting the

magnitude of the additional LLW stream that would result from

the disposal of dry-storage canisters, and it is not included in this

analysis.

A breakdown of these waste streams is as follows:

Scenario 2: Repository Only

LLW – 56,000 m3

Scenario 3: Repository, Reprocessing, Recycling of Plutonium and

Uranium

From Reprocessing Operations

LLW – 441,000 m3

Mixed LLW15 – 2,000 m3

GTCC waste – 12,000 m3

Mixed GTCC waste – 7,000 m3

From Repository Operations

LLW – 48,000 m3

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U.S. Nuclear Waste Technical Review Board

15.Mixed LLW and Mixed GTCC waste mean LLW and GTCC waste, respectively, that has

chemical contents outside the usual specification for these wastes and may require additional

packaging or disposal in accordance with the terms of the Resource Conservation and

Recovery Act.
Scenario 4: Repository, Reprocessing, Recycling of Plutonium

From Reprocessing Operations

LLW – 464,000 m3

Mixed LLW – 2,000 m3

GTCC waste – 13,000 m3

Mixed GTCC waste – 7,000 m3

From Repository Operations

LLW – 58,000 m3

From these figures, it is apparent that LLW represents by far the

largest component (more than 95 percent) of these waste streams

that would be generated by reprocessing. However, it is

important to note that it may be necessary to develop a

below-surface disposal facility for GTCC waste. This would likely

take longer, and be a more complex undertaking, than developing

the additional disposal capacity required for the LLW.

Other Considerations

Other consequences of different fuel-cycle options also can be

evaluated using NUWASTE. For example, NUWASTE projects

the quantity of plutonium that would be separated during

reprocessing.

Figure 6 shows how much plutonium would be separated on a

cumulative basis by adopting either Scenario 3 or Scenario 4.

From Figure 6, it is apparent that unless the fabrication and use of

MOX fuel are managed successfully, a large plutonium stockpile

would be created, potentially giving rise to proliferation concerns.

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Nuclear Waste Assessment System for Technical Evaluation (NUWASTE) Status and Initial Results
Ongoing Activities

The Board is in the process of extending this analysis and

increasing the scope and functionality of NUWASTE. Near-term

plans include evaluating additional LWR scenarios and adding

the capability to evaluate the relative effects of different fuel-cycle

options on program costs and the operational timelines for the

SNF management and waste disposal facilities required.

Longer-term plans include expanding NUWASTE capability to:

Analyze the waste-related effects of introducing advanced

thermal reactors (Gen III and Gen IV types) and fast reactors.

Evaluate the effect of adopting alternative reprocessing

technologies.

Include the disposal of all DOE-owned SNF and HLW.

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U.S. Nuclear Waste Technical Review Board

Figure 6. Quantity of Plutonium Separated by Reprocessing
Project the capacities of away-from-reactor storage facilities

that would be required for a range of centralized-storage

scenarios.

Estimate the transportation requirements at each stage of the

fuel cycle.

As these developments are implemented, the Board will continue

to report the results of its analyses to inform Congress, DOE, and

other interested parties.

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Nuclear Waste Assessment System for Technical Evaluation (NUWASTE) Status and Initial Results
Glossary

Actinides. Elements with atomic numbers of 89 to 103. All actinides are radioactive,

and all of the actinides in SNF are produced during reactor operation, with the sole

exception of uranium and plutonium remaining from when the fuel was fabricated.

BWR. Boiling-water reactor.

Enrichment. Natural uranium contains approximately 0.7 percent of the isotope 235U.

For use in the fabrication of LWR fuel, uranium must contain, typically, between

3 percent and 5 percent 235U. The process used to increase the percentage of 235U is

called “enrichment.”

Fission products. Isotopes that result from the fission (splitting) of atoms of heavy

elements, such as uranium and plutonium: for example, iodine-131 (131I) and

strontium-90 (90Sr).

Fuel burn-up. See GWd/MT

GTCC waste. Greater-Than-Class-C (GTCC) waste is similar in origin, and in the

types of materials it contains, to LLW. However, the concentrations of radionuclides

in GTCC waste make it generally unacceptable for near-surface disposal.

Consequently, GTCC waste may require disposal in an underground facility and

could be co-disposed of in a deep geologic repository with HLW.

GWd/MT. Gigawatt days per metric ton (of fuel): a measure of the energy that has

been produced by fuel (also referred to as the “burn-up" of the fuel) during reactor

operation.

HLW. High-level radioactive waste: the primary waste stream from reprocessing –

including, fission products and minor actinides, that can be vitrified into a solid glass

waste form in high-integrity canisters that are suitable for repository disposal.

Light water. Water found in nature is essentially all “light water.” Light water

comprises two atoms of hydrogen and one atom of oxygen and has the molecular

symbol “H2O.” Deuterium is a heavy isotope of hydrogen but is chemically similar to

hydrogen. Thus, water also can comprise two deuterium atoms and one oxygen atom.

In this form, it has the molecular symbol D2O. Because deuterium is heavier than

hydrogen, D2O is referred to as “heavy water,” which is required for the operation of

some nuclear power plants. Consequently, LWRs are so called to make the distinction

between them and reactors that require heavy water.

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U.S. Nuclear Waste Technical Review Board
LLW. Low-level waste: materials with various physical and chemical characteristics

and a range of concentrations of radioactive isotopes. It typically comprises mainly

items such as coveralls, reactor water treatment residues, tools, and equipment, that

have become contaminated with radioactive materials or have become radioactive

through exposure to neutron radiation. The U.S. Nuclear Regulatory Commission

classifies LLW in Classes A, B, and C, according to the concentrations of specific

radionuclides, which are all suitable for disposal in near-surface disposal facilities.

LWR. Light-water reactor: BWRs and PWRs are light-water reactors. All nuclear

power plants currently operating in the United States are LWRs.

Material balance. A method of accounting for nuclear materials as they move

through the fuel-cycle operations in a scenario, in order to ensure that all material is

recorded. This is similar to periodically balancing a bank account during a series of

financial transactions.

MOX fuel. “Mixed oxide” fuel: fuel fabricated using a blend of plutonium oxide

from SNF separated by reprocessing and uranium oxide. MOX fuel can be made

using natural uranium, tails from enrichment, or uranium separated from SNF by

reprocessing.

MT/yr. Metric tons per year.

PWR. Pressurized-water reactor.

Recycled tails. The tails resulting from enriching reprocessed uranium during

recycling.

Recycling. Production of MOX fuel using plutonium from SNF separated by

reprocessing and/or production of uranium fuel using re-enriched uranium separated

from SNF by reprocessing.

Reprocessing. A process involving dissolution of SNF and chemical separation of the

dissolved contents of the fuel into a uranium product stream, a plutonium product

stream, a high-level radioactive waste stream, and a fission product gases waste

stream. The uranium and plutonium products can be used for fabricating new fuel.

SNF. Spent nuclear fuel: Nuclear fuel that has been used in a reactor to generate

power. Following discharge from a reactor, spent nuclear fuel may be reprocessed or

disposed of directly in a repository.

Tails. The objective of enrichment is to produce uranium with an increased 235U

content than in natural uranium. The by-product of enrichment is a uranium waste

stream with a reduced, or “depleted,” 235U content. This material is referred to as

“tails.”

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Nuclear Waste Assessment System for Technical Evaluation (NUWASTE) Status and Initial Results
U.S. Nuclear Waste Technical Review Board

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